Novel metal insulator metal capacitors based on electrosprayed colloidal nanoparticles

Tesi en modalitat de compendi de publicacions. Aplicat embargament des de la data de defensa fins el 7/1/2022This work develops a novel capacitor device based on the use of nanotechnology. The device starts from the exiting metal-insulator-metal (MIM) concept, but instead of a continuous insulator layer, dielectric nanoparticles are used. Nanoparticles are mainly of silicon oxide (silica) and polystyrene (PS) and the diameter values are 255nm and 295nm respectively. The nanoparticles contribute to a very high surface to volume ratio and are easily available at low cost. The deposition technique developed in this work is the electrospray, which is a bottom-up fabrication technology that allows batch processing and achieves a good compromise between large area and low deposition time. With the objective of increasing the deposit surface, the electrospray set-up has been tuned to allow deposition areas from 1cm2 to 25cm2. The fabricated devices, the so called nanoparticles metal insulator metal (NP-MIM) capacitors, offer higher capacitance values than a similar conventional capacitor with a continuous insulator layer. In the case of silica NP-MIMs, a factor as high as 1000 of capacitance enhancement is achieved, whereas polystyrene NP-MIMs has capacitance gain of 11. In addition, silica NP-MIMs show capacitive behaviours in a certain frequency range which depends on the humidity and thickness of the nanoparticles layer, while polystyrene MIMs always maintain their capacitive behaviour. The fabricated devices have been characterized by scanning electron microscopy (SEM) measurements complemented with focusing ion beam (FIB) drilling to characterise the topography of the NP-MIMs. The devices have also been characterized by impedance spectroscopy measurements, at different temperatures and humidifies. The origin of the enhanced capacitance is associated in part to humidity in the nanoparticles interfaces. A circuital model based on distributed elements has been developed to fit and predict the electrical behaviour of the NP-MIMs. In summary, this thesis shows the design, fabrication, characterization and modelling of a new promising nanoparticles metal-insulator-metal capacitor that may pave the way to the development of a novel MIM-supercapacitor technology.Este trabajo desarrolla un novedoso dispositivo condensador basado en el uso de la nanotecnología. El dispositivo parte del concepto existente de metal-aislador-metal (MIM), pero en lugar de una capa aislante continua, se utilizan nanopartículas dieléctricas. Las nanopartículas son principalmente de óxido de silicio (sílice) y poliestireno (PS) y los valores de diámetro son 255nm y 295nm respectivamente. Las nanopartículas contribuyen a una alta relación superficie/volumen y están fácilmente disponibles a bajo costo. La técnica de depósito desarrollada en este trabajo es el electrospray, que es una tecnología de fabricación ascendente (bottom-up) que permite el procesamiento por lotes y logra un buen compromiso entre una gran superficie y un bajo tiempo de depósito. Con el objetivo de aumentar la superficie de depósito, la configuración de electrospray ha sido ajustada para permitir áreas de depósito de 1cm2 a 25cm2. El dispositivo fabricado, los llamados condensadores de metal aislante de nanopartículas (NP-MIM) ofrecen valores de capacitancia más altos que un condensador convencional similar con una capa aislante continua. En el caso de los NP-MIM de sílice, se alcanza un factor de hasta 1000 de mejora de la capacidad, mientras que los NP-MIM de poliestireno tienen una ganancia de capacidad de 11. Además, los NP-MIM de sílice muestran comportamientos capacitivos en un cierto rango de frecuencias que depende de la humedad y el grosor de la capa de nanopartículas, mientras que los MIM de poliestireno siempre mantienen su comportamiento capacitivo. Los dispositivos fabricados se han caracterizado por mediciones de microscopía electrónica de barrido (SEM) complementadas con perforaciones de haz de iones de enfoque (FIB) para caracterizar la topografía de los NP-MIMs. Los dispositivos también se han caracterizado por mediciones de espectroscopia de impedancia, a diferentes temperaturas y humedades. El origen de la capacitancia aumentada está asociado en parte a la humedad en las interfaces de las nanopartículas. Se ha desarrollado un modelo de un circuito basado en elementos distribuidos para ajustar y predecir el comportamiento eléctrico de los NP-MIMs. En resumen, esta tesis muestra el diseño, fabricación, caracterización y modelización de un nuevo y prometedor condensador nanopartículas metal-aislante-metal que puede allanar el camino para el desarrollo de una nueva tecnología de supercondensadores MIM.Postprint (published version

Ultrathin CaTiO3 Capacitors: Physics and Application

Scaling of electronic circuits from micro- to nanometer size determined the incredible development in computer technology in the last decades. In charge storage capacitors that are the largest components in dynamic random access memories (DRAM), dielectrics with higher permittivity (high-k) were needed to replace SiO2. Therefore ZrO2 has been introduced in the capacitor stack to allow sufficient capacitance in decreasing structure sizes. To improve the capacitance density per cell area, approaches with three dimensional structures were developed in device fabrication. To further enable scaling for future generations, significant efforts to replace ZrO2 as high-k dielectric have been undertaken since the 1990s. In calculations, CaTiO3 has been identified as a potential replacement to allow a significant capacitance improvement. This material exhibits a significantly higher permittivity and a sufficient band gap. The scope of this thesis is therefore the preparation and detailed physical and electrical characterization of ultrathin CaTiO3 layers. The complete capacitor stacks including CaTiO3 have been prepared under ultrahigh vacuum to minimize the influence of adsorbents or contaminants at the interfaces. Various electrodes are evaluated regarding temperature stability and chemical reactance to achieve crystalline CaTiO3. An optimal electrode was found to be a stack consisting of Pt on TiN. Physical experiments confirm the excellent band gap of 4.0-4.2 eV for ultrathin CaTiO3 layers. Growth studies to achieve crystalline CaTiO3 indicate a reduction of crystallization temperature from 640°C on SiO2 to 550°C on Pt. This reduction has been investigated in detail in transmission electron microscopy measurements, revealing a local and partial epitaxial growth of (111) CaTiO3 on top of (111) Pt surfaces. This preferential growth is beneficial to the electrical performance with an increased relative permittivity of 55 with the advantage of a low leakage current comparable to that in amorphous CaTiO3 layers. A detailed electrical analysis of capacitors with amorphous and crystalline CaTiO3 reveals a relative permittivity of 30 for amorphous and an excellent value of 105 for fully crystalline CaTiO3. The permittivity exhibits a quadratic dependence with applied electric field. Crystalline CaTiO3 shows a 1-3% drop in capacitance density and permittivity at a bias voltage of 1V, which is significantly lower compared to all results for SrTiO3 capacitors measured elsewhere. A capacitance equivalent thickness (CET) below 1.0 nm with current densities 1×10−8 A/cm2 have been achieved on carbon electrodes. Finally, CETs of about 0.5 nm with leakage currents of 1 × 10−7 A/cm2 on top of Pt/TiN fulfill the 2016 DRAM requirements following the ITRS road map of 2012.Die Verkleinerung von elektronischen Bauelementen hin zu nanometerkleinen Strukturen beschreibt die unglaubliche Entwicklung der Computertechnologie in den letzten Jahrzehnten. In Ladungsspeicherkondensatoren, den größten Komponenten in Arbeitsspeichern, wurden dafür Dielektrika benötigt, die eine deutlich höhere Permittivität als SiO2 besitzen. ZrO2 wurde als geeignetes Dielektrikum eingeführt, um eine ausreichende Kapazität bei kleiner werdenen Strukturen sicherzustellen. Zur weiteren Verbesserung der Kapazitätsdichte pro Zellfläche konnten 3D Strukturen in die Chipherstellung integriert werden. Seit den 1990ern wurden parallel bedeutende Anstrengungen unternommen, um ZrO2 als Dielektrikum durch Materialien mit noch höherer Permittivität zu ersetzen. Nach Berechnungen stellt nun CaTiO3 eine mögliche Alternative dar, die eine weitere Verbesserung der Kapazität ermöglicht. Das Material besitzt eine deutlich höhere Permittivität und eine ausreichend große Bandlücke. Diese Arbeit beschäftigt sich deshalb mit Herstellung und detaillierter physikalischer und elektrischer Charakterisierung von extrem dünnen CaTiO3 Schichten. Zusätzlich wurden diverse Elektroden bezüglich ihrer Temperaturstabilität und der chemischen Stabilität untersucht, um kristallines CaTiO3 zu herhalten. Als eine optimale Elektrode stellte sich Pt auf TiN heraus. Physikalische Experimente an extrem dünnen CaTiO3 Schichten bestätigen die Bandlücke von 4,0-4,2 eV. Wachstumsuntersuchungen an kristallinem CaTiO3 zeigen eine Reduktion der Kristallisationstemperatur von 640°C auf SiO2 zu 550°C auf Pt. Diese Reduktion wurde detailliert mittels Transmissionselektronenmikroskopie untersucht. Es konnte für einige Schichten ein partielles lokales epitaktischesWachstum von (111) CaTiO3 auf (111) Pt gemessen werden. Dieses Vorzugswachstum ist vorteilhaft für die elektrischen Eigenschaften durch eine gesteigerte Permittivität von 55 bei gleichzeitig geringem Leckstrom vergleichbar zu amorphen Schichten. Eine genaue elektrische Analyse von Kondensatoren mit amorphen und kristallinem CaTiO3 ergibt eine Permittivität von 30 für amorphe und bis zu 105 für kristalline CaTiO3 Schichten. Die Permittivität zeigt eine quadratische Abhängigheit von der angelegten Spannung. Kristallines CaTiO3 zeigt einen 1-3% Abfall der Permittivität bei 1V, der wesentlich geringer ausfällt als vergleichbare Werte für SrTiO3. Eine zu SiO2 vergleichbare Schichtdicke (CET) von unter 1,0 nm mit Stromdichten von 1×10−8 A/cm2 wurde auf Kohlenstoffsubstraten erreicht. Mit Werten von 0,5 nm bei Leckstromdichten von 1×10−7 A/cm2 auf Pt/TiN Elektroden erfüllen die CaTiO3 Kondensatoren die Anforderungen der ITRS Strategiepläne für Arbeitsspeicher ab 2016

Aatomkihtsadestatud tsirkooniumipõhiste nanolaminaatide ja segukilede magnetilised, elektrilised ja struktuursed omadused

Väitekirja elektrooniline versioon ei sisalda publikatsiooneDoktoritöös kasutati aatomkihtsadestamise meetodit, eesmärgiga valmistada multiferroidne nanoskaalas kile, ehk paarikümne nanomeetri paksune materjalikiht. Multiferroid on selline materjal, mis on üheaegselt nii ferromagnetiline kui ka ferroelektriline, st polariseerub nii välises magnet- kui ka elektriväljas ning on võimeline mõlemat polarisatsiooni säilitama ka välise välja eemaldamisel. Sellist materjali oleks võimalik kasutada uue põlvkonna nanoelektroonikas, näiteks mäluseadmete valmistamiseks. Aatomkihtsadestamise meetod valiti, kuna see on ennast tõestanud, kui üks sobivamaid viise üliõhukeste tahkiskihtide valmistamiseks ühtlase paksuse ja koostisega üle suure pinna. Kirjandusallikate põhjal oli teada, et materjali valmistamine, mis oleks üheaegselt nii ferromagnetiline kui ka ferroelektriline, ei ole lihtne ülesanne. Nimetatud nähtusi on tuvastatud ühe materjali samas faasis ainult ülimadalatel temperatuuridel ja/või suurtes materjalitükkides. Autorile teadaolevalt ei ole multiferroidi suudetud valmistada õhukese materjalikihina ning toimivana ka toatemperatuuril või kõrgemal. Mõlemad nimetatud tingimused on kindlasti tarvilikud, et rääkida võimalikest praktilistest rakendustest. Erinevates ZrO2 sisaldavates kiledes demonstreeriti osa kilede puhul ferromagnetilist hüstereesi ning osa käitus elektriväljas ferroelektrikule sarnaselt. Ühel juhul tuvastati ferromagnetiline ja ferroelektriline polariseeritavus samas kilenäidises. Järeldati, et kuigi traditsioonilisest ferromagnetismist rääkimiseks ei ole nanoskaalas metalloksiidkilede puhul põhjust, siis teatud juhtudel võivad siiski defektid, nagu näiteks hapnikuvakantsid, materjali ferromagnetilist käitumist põhjustada. Kuigi defektid raskendavad ferroelektrilise polarisatsiooni mõõtmist, võib leida nö. tasakaalupunkti piisava hulga defektide vahel, et saavutada ferromagnetiline polarisatsioon ja piisavalt vähese hulga defektide vahel, et ferroelektriline efekt ei jää veel täielikult piirpindadel tekkiva lekkevoolust tingitud polarisatsiooni varju. Autori arvates tuvastati selline olukord, kui defektirohke ferromagnetiline ZrO2 segati vähem defektse materjaliga HfO2, mille puhul võis kirjandusele toetudes oodata ferroelektrilisust.The main goal was to fabricate a multiferroic nanoscale film using atomic layer deposition. Multiferroic is a material that is both ferromagnetic and ferroelectric, that is, polarizes in both magnetic and electric fields, and retains that polarization after removing the external field. Such a material could be used in novel nanoelectronics applications, such as memory devices or sensors. Atomic layer deposition was chosen to fabricate the films, because this is the method actually used in modern nanoelectronics to deposit ultrathin films, and the only method which can provide conformal films over a large substrate area and at the same time provide thickness control at the nanometer level. It was known beforehand, from literature, that a material possessing ferromagnetic and ferroelectric behavior in the same sample in the same phase will be a difficult task. This phenomenon has been observed in bulk materials and/or very low temperatures, but not in thin films and at room temperature, which are both necessary, if one wishes to consider an actual nanoelectronics application. In various ZrO2-based thin films, it was shown that some films showed ferromagnetic hysteresis and some exhibited behavior resembling ferroelectric response. In one case, ferromagnetic and ferroelectric behavior were observed in the same material sample. It was concluded that although one cannot speak of ferromagnetism in the traditional sense, when thin metal oxide films are studied, but in certain cases, ferromagnetism may still arise from the defects of a material, such as oxygen vacancies. Although these defects make the detection of ferroelectricity harder, a reasonable trade-off can be found between enough defects to induce ferromagnetism and not so much to overwhelm the signs of ferroelectricity completely. The author believes such as case was found, when a defective material, which was found ferromagnetic in all cases, namely ZrO2, was mixed with a less defective material, HfO2, known already in literature to be ferroelectric in some cases.https://www.ester.ee/record=b536107

The planar anodic Al2O3-ZrO2 nanocomposite capacitor dielectrics for advanced passive device integration

The need for integrated passive devices (IPDs) emerges from the increasing consumer demand for electronic product miniaturization. Metal-insulator-metal (MIM) capacitors are vital components of IPD systems. Developing new materials and technologies is essential for advancing capacitor characteristics and co-integrating with other electronic passives. Here we present an innovative electrochemical technology joined with the sputter-deposition of Al and Zr layers to synthesize novel planar nanocomposite metal-oxide dielectrics consisting of ZrO2 nanorods self-embedded into the nanoporous Al2O3 matrix such that its pores are entirely filled with zirconium oxide. The technology is utilized in MIM capacitors characterized by modern surface and interface analysis techniques and electrical measurements. In the 95-480 nm thickness range, the best-achieved MIM device characteristics are the one-layer capacitance density of 112 nF center dot cm(-2), the loss tangent of 4 center dot 10(-3) at frequencies up to 1 MHz, the leakage current density of 40 pA center dot cm(-2), the breakdown field strength of up to 10 MV center dot cm(-1), the energy density of 100 J center dot cm(-3), the quadratic voltage coefficient of capacitance of 4 ppm center dot V-2, and the temperature coefficient of capacitance of 480 ppm center dot K-1 at 293-423 K at 1 MHz. The outstanding performance, stability, and tunable capacitors' characteristics allow for their application in low-pass filters, coupling/decoupling/bypass circuits, RC oscillators, energy-storage devices, ultrafast charge/discharge units, or high-precision analog-to-digital converters. The capacitor technology based on the non-porous planar anodic-oxide dielectrics complements the electrochemical conception of IPDs that combined, until now, the anodized aluminum interconnection, microresistors, and microinductors, all co-related in one system for use in portable electronic devices

Total Ionizing Dose Response of High-k Dielectrics on MOS Devices

As advanced Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) technology continues to minimize the gate oxide thickness, the exponential increase in gate leakage current poses a major challenge for silicon dioxide (SiO2) based devices. In order to reduce the gate leakage current while maintaining the same gate capacitance, alternative gate insulator materials with higher dielectric constant (high-k) became the preferred replacement of SiO2 gate dielectrics. Germanium (Ge) MOSFETs have been regarded as promising candidates for future high-speed applications because they possess higher carrier mobility when compared to silicon based devices. At present, advanced microelectronics devices and circuits are used in aerospace engineering, nuclear industry, and radiotherapy equipment. These applications are unavoidably exposed to space-like radiation, which has a relative low radiation dose rate at 10-2-10-6 rad(Si)/s. For these reasons, it is necessary to understand the low-dose-rate radiation response of high-k materials based on Si and Ge MOS devices. The radiation response of high-k materials such as radiation-induced oxide and interface trap density have been typically examined by carrying out off-site capacitance-voltage (CV) measurements. However, the conventional and off-site radiation response measurements may underestimate the degradation of MOS devices. In this study, a semi-automated laboratory-scale real-time and on-site radiation response testing system was developed to evaluate the radiationresponse. The system is capable of estimating the radiation response of MOS devices whilst the devices are continuously irradiated by -rays raysrays. Moreover, the complete CV characteristics of MOS capacitors were measured in a relatively short time. The pulse CV measurement reduces the impact of charge trapping behavior on the measurement results, when compared to conventional techniques. The total ionizing dose radiation effect on HfO2 dielectric thin films prepared by atomic layer deposition (ALD) has been investigated by the proposed measurement system. The large bidirectional ΔVFB of the irradiated HfO2 capacitor was mainly attributed to the radiation-induced oxide trapped charges, which were not readily compensated by bias-induced charges produced over the measurement timescales of less than 5 ms. Radiation response of Ge MOS capacitors with HfO2 and HfxZr1-xOy gate dielectrics was also investigated. It was found that radiation-induced interface traps were the dominant factor for Flat-band Voltage shift (ΔVFB) in HfO2 thin films, whereas the radiation response for Zr-containing dielectrics under positive bias was mainly affected by oxide traps. Under positive biased irradiation, the Zr-doped HfxZr1-xOy exhibited smaller ΔVFB than that of HfO2. This is attributed to the de-passivation of Ge-S bonds in capacitors incorporating HfO2 thin films, resulting in the build-up of interface traps. Under negative biased irradiation, ΔVFB was attributed to the combined effect of the net oxide trapped charges and the passivation of Ge dangling bonds at the Ge/high-k interface